1. Field of the Invention
This invention relates to one-part polyurethane adhesives which are curable upon exposure to ambient moisture and to methods for making same.
One-part polyurethane adhesives typically are produced by reacting a polyether diol, triol, tetrol or mixtures thereof with a polyisocyanate, with or without a catalyst, in a reactor for up to eight hours to produce an isocyanate-terminated prepolymer. Various additives are blended with the prepolymer to provide a product having the desired characteristics and the resulting product is packaged in substantially hermetically sealed containers for use.
II. Prior Art
Because of the reactivity of water with isocyanates, it is common practice to take steps to avoid the inclusion of water during processing. To accomplish this, the processing is typically carried out in a sealed container under a blanket of inert gas, such as nitrogen, and fillers and other materials used in the formulation are dried to a substantially anhydrous condition prior to use. In another approach exemplified by Coyner et al. U.S. Pat. Nos. 3,919,173 and 4,038,239, an alkaline earth metal oxide, such as calcium oxide or calcium carbonate, is included in the formulation as a de-watering agent for scavenging water from the polyol and water of hydration or physically bound water in fillers, plasticizers, pigments, etc.